Regulation of
 Aggregatibacter
 (
 Actinobacillus
 )
 actinomycetemcomitans
 Leukotoxin Secretion by Iron

Balashova, Nataliya V.; Diaz, Roger; Balashov, Sergey; Crosby, Juan A.; Kachlany, Scott C.

doi:10.1128/jb.01253-06

Cited by 33 publications

(36 citation statements)

References 46 publications

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“…The growth medium was TSBYE (3% tryptic soy broth plus 0.6% yeast extract) containing, when needed to select for transformants, spectinomycin (Spec) to a final concentration of 100 g/ml or ampicillin to a final concentration of 10 g/l. In experiments where leukotoxin protein levels were evaluated, 300 M FeCl 3 was included in the medium to suppress leukotoxin secretion (39).…”

Section: Methodsmentioning

confidence: 99%

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

et al. 2013

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Aggregatibacter actinomycetemcomitans, a periodontal pathogen, synthesizes leukotoxin (LtxA), a protein that helps the bacterium evade the host immune response. Transcription of the ltxA operon is induced during anaerobic growth. The cyclic AMP (cAMP) receptor protein (CRP) indirectly increases ltxA expression, but the intermediary regulator is unknown. Integration host factor (IHF) binds to and represses the leukotoxin promoter, but neither CRP nor IHF is responsible for the anaerobic induction of ltxA RNA synthesis. Thus, we have undertaken studies to identify other regulators of leukotoxin transcription and to demonstrate how these proteins work together to modulate leukotoxin synthesis. First, analyses of ltxA RNA expression from defined leukotoxin promoter mutations in the chromosome identify positions ؊69 to ؊35 as the key control region and indicate that an activator protein modulates leukotoxin transcription. We show that Mlc, which is a repressor in Escherichia coli, functions as a direct transcriptional activator in A. actinomycetemcomitans; an mlc deletion mutant reduces leukotoxin RNA synthesis, and recombinant Mlc protein binds specifically at the ؊68 to ؊40 region of the leukotoxin promoter. Furthermore, we show that CRP activates ltxA expression indirectly by increasing the levels of Mlc. Analyses of ⌬mlc, ⌬ihf, and ⌬ihf ⌬mlc strains demonstrate that Mlc can increase RNA polymerase (RNAP) activity directly and that IHF represses ltxA RNA synthesis mainly by blocking Mlc binding. Finally, a ⌬ihf ⌬mlc mutant still induces ltxA during anaerobic growth, indicating that there are additional factors involved in leukotoxin transcriptional regulation. A model for the coordinated regulation of leukotoxin transcription is presented.

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Section: Methodsmentioning

confidence: 99%

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

et al. 2013

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“…Thus, JP2 strains have an impaired ability to utilize complexed iron from host proteins. We have proposed that perhaps high leukotoxicity (and hence deletion of the promoter region) was strongly selected for in these strains that lacked HgpA, resulting in the JP2 phenotype (Balashova et al, 2006b). Increased lysis of RBCs would result in greater release of heme and hemoglobin and a more favorable chance that some could be used by the bacterium.…”

Section: Ironmentioning

confidence: 99%

“…Indeed, iron regulates secretion, not transcription, of LtxA (Balashova et al, 2006b). In the presence of excess iron, but not other metal ions, LtxA remains intracellular; but under iron-limiting conditions, LtxA is essentially fully secreted.…”

Section: Ironmentioning

confidence: 99%

Aggregatibacter actinomycetemcomitansLeukotoxin

2010

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Aggregatibacter actinomycetemcomitans is a Gram-negative bacterium that colonizes the human oral cavity and is the causative agent for localized aggressive periodontitis (LAP), an aggressive form of periodontal disease that occurs in adolescents. A. actinomycetemcomitans secretes a protein toxin, leukotoxin (LtxA), which helps the bacterium evade the host immune response during infection. LtxA is a membrane-active toxin that specifically targets white blood cells (WBCs). In this review, we discuss recent developments in this field, including the identification and characterization of genes and proteins involved in secretion, regulation of LtxA, biosynthesis, newly described activities of LtxA, and how LtxA may be used as a therapy for the treatment of diseases.

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“…In addition, we have recently shown that LtxA can act as a hemolysin that may be used during systemic infection for acquiring iron from the host (2). Indeed, iron, but not other metals, regulates LtxA secretion in A. actinomycetemcomitans (3).…”

mentioning

confidence: 99%

Screen for Leukotoxin Mutants in Aggregatibacter actinomycetemcomitans : Genes of the Phosphotransferase System Are Required for Leukotoxin Biosynthesis

et al. 2008

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Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans is a pathogen that causes localized aggressive periodontitis and extraoral infections including infective endocarditis. Recently, we reported that A. actinomycetemcomitans is beta-hemolytic on certain growth media due to the production of leukotoxin (LtxA). Based on this observation and our ability to generate random transposon insertions in A. actinomycetemcomitans, we developed and carried out a rapid screen for LtxA mutants. Using PCR, we mapped several of the mutations to genes that are known or predicted to be required for LtxA production, including ltxA, ltxB, ltxD, and tdeA. In addition, we identified an insertion in a gene previously not recognized to be involved in LtxA biosynthesis, ptsH. ptsH encodes the protein HPr, a phosphocarrier protein that is part of the sugar phosphotransferase system. HPr results in the phosphorylation of other proteins and ultimately in the activation of adenylate cyclase and cyclic AMP (cAMP) production. The ptsH mutant showed only partial hemolysis on blood agar and did not produce LtxA. The phenotype was complemented by supplying wild-type ptsH in trans, and real-time PCR analysis showed that the ptsH mutant produced approximately 10-fold less ltxA mRNA than the wild-type strain. The levels of cAMP in the ptsH mutant were significantly lower than in the wild-type strain, and LtxA production could be restored by adding exogenous cAMP to the culture.

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Regulation of Aggregatibacter ( Actinobacillus ) actinomycetemcomitans Leukotoxin Secretion by Iron

Cited by 33 publications

References 46 publications

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

Mlc Is a Transcriptional Activator with a Key Role in Integrating Cyclic AMP Receptor Protein and Integration Host Factor Regulation of Leukotoxin RNA Synthesis in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitansLeukotoxin

Screen for Leukotoxin Mutants in Aggregatibacter actinomycetemcomitans : Genes of the Phosphotransferase System Are Required for Leukotoxin Biosynthesis

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